1. Field of the Invention
This invention relates to a light-receiving module, in which an optical signal is converted into an electrical signal.
2. Related Prior Art
As shown in FIG. 9 and FIG. 10, a conventional light-receiving module has a semiconductor light-receiving device 102, such as a photodiode, a base 103 for mounting the light-receiving device 102, and a plurality of lead terminals 104 to 108. The semiconductor light-receiving device converts an incident optical signal to a corresponding electrical signal. The base 102 also mounts a semiconductor electronic device that amplifies the converted electrical signal and outputs the signal to an outside of the module through the lead terminal. A sealing material 109, such as a glass sealant, supports the lead terminals 104 to 108 that are not connecting to the base 103. The sealing material electrically isolates the lead terminals 104 to 108 from the base 102. In the conventional module, the base made of metal forms a hollow 110 in its backside opposing to the surface where the semiconductor device is mounted thereon. The sealing material is entirely filled up within the hollow.
The current optical communication requires a transmission speed over 10 Gbps. In such high-speed application, the conventional optical module shown in FIGS. 9 and 10 can not be applicable because a lead terminal through which an electrical signal is transmitted has not an impedance-matched configuration. When the electrical signal transmits such lead terminal, a reflection and a loss of the signal may occur at an impedance-mismatched portion. The higher the transmission speeds, the more serious this impedance-mismatched problem. Moreover, the higher the transmission speeds, the more the power consumption of the semiconductor device. In the conventional module, since the backside of the base is entirely filled up with the sealant that has less thermal conductivity than metal, the heat dissipation through the base is restricted.
One aspect of the present invention is a light-receiving assembly comprising a light-receiving module and a circuit board installed the a light-receiving module thereon. The light-receiving module includes a semiconductor light-receiving device such as semiconductor photodiode, a first and a second lead terminals and a metal body. The semiconductor light-receiving device converts an optical signal input therein to an electrical signal. The circuit board has a signal transmission line on the first surface and bias supply lines on the second surface opposite of the first surface. The first lead terminal outputs an electrical signal and the second lead terminal provides an electrical bias to the semiconductor light-receiving device within the module. The metal body has a plurality of through holes, the first and the second lead terminal pass therethrough with a sealant being plugged into the gap between the surface of the through hole and the lead terminal. The circuit board is sandwiched by the first lead terminal and the second lead terminal. The first lead terminal is connected to the transmission line of the first surface such that the first lead terminal is straitened, while the second lead terminal is connected to the bias supply lines on the second surface.
In the present invention, the second lead terminal may be bent to the bias supply lines of the second surface of the circuit board. Moreover, the diameter of the first lead terminal may be smaller than that of the second lead terminal. Therefore, the first lead terminal may be impedance-matched at the through hole by adjusting the gap to the inner surface of the through hole and the dielectric constant of the sealant plugged in the through hole.
In this assembly, the electrical signal converted by the semiconductor device is transmitted to the first lead terminal, the impedance of which may be matched at the portion of the through hole, and finally transferred to the transmission line on the first surface of the board. Since the metal body of the module abuts on or just close to the edge of the circuit board and the first lead terminal is connected to the transmission line such that the first lead terminal is straitened, the reflection and the loss of the transmission signal can be restricted.